Abstract
Seasonal variations in dissolved organic matter (DOM) fluxes from land to sea have been well documented in the Arctic, yet remarkably little is known about how DOM varies seasonally within Arctic coastal waters. This is particularly true for shallow inshore environments. Here we document seasonality of DOM in lagoons along the eastern Alaska Beaufort Sea coast during the spring ice break‐up (June), summer open‐water (August), and late winter ice‐covered (April) periods. We measured dissolved organic carbon (DOC) concentrations, C:N ratios, and chromophoric DOM (CDOM) characteristics (SUVA 254 and S 275–295 ). On average, lagoon DOC was highest during spring (~200 μ M) and lowest during winter (~120 μ M). C:N and SUVA 254 also differed markedly between spring (C:N ~ 28; SUVA 254 ~ 3.5 L mg C −1 m −1 ) and winter (C:N ~ 16; SUVA 254 ~ 2.2 L mg C −1 m −1 ). Average S 275–295 values (~14–17 × 10 −3 nm −1 ) were not significantly different among seasons, but variability in S 275–295 was much lower in spring. This was attributed to terrestrial runoff based on its relatively uniform composition during the spring freshet. Seasonal variations in lagoon DOM were broadly correlated with variations in salinity (i.e., lagoon water transitioned from largely fresh in spring to hypersaline in winter), but a mixing analysis revealed strong evidence of processing and net DOC generation in summer. We also found evidence of DOC processing and build‐up under the ice over the winter. This baseline understanding of DOM seasonality in Arctic lagoons is essential for evaluating climate‐linked impacts on Arctic coastal ecosystems and broader feedbacks associated with carbon cycling.